A slow-moving storm system that’s been called an atmospheric river is poised to deliver bouts of heavy rain across the Mid-Atlantic over the next few days, increasing the risk of flash floods.
Forecasters expressed concern for areas where the ground is especially vulnerable in North Carolina. David Roth, a meteorologist at the Weather Prediction Center, said the state has been particularly at risk since Hurricane Helene.
“Helene just made everything worse,” he said. “There were some landslides in western North Carolina from it. It takes a while to recover from a tropical cyclone. So their ground is more sensitive.”
Mr. Roth said North Carolina’s complex terrain was another factor of concern.
“They have a lot of up and down variation,” he said. “Even without Helene, almost every time it rains moderately, to have the mountains, basically you get these small waterfalls.”
The Weather Prediction Center has issued a Level 2 out of 4 risk for excessive rainfall, potentially leading to flash flooding across eastern North Carolina, eastern Virginia, Maryland, eastern West Virginia and extending into central and southern Pennsylvania through Wednesday.
Flood watches have been issued across these areas through late Tuesday.
Rainfall totals were expected to range between one and three inches, and rain may fall at a rate of one to two inches an hour. Forecasters anticipated the intense rain to develop by late Tuesday morning, fueled by daytime warming.
The Weather Prediction Center also noted that the hills and mountains stretching from southern Pennsylvania through Virginia could receive additional rainfall because of the way the air is being pushed up the slopes. Recent rainfall has saturated the ground in this region, further elevating the risk of flash flooding.
The storm has brought repeated rounds of heavy rain to the Southeast since last week. Its slow-moving nature and a continuous feed of moisture from the Gulf and Atlantic are the main risk factors for flash floods.
Forecasters have called this an atmospheric river, a term more commonly associated with the steady streams of moisture that soak the West Coast but that also describes patterns responsible for rain in the East.
“You can call any warm conveyor belt circulation around a nontropical low an atmospheric river,” said Mr. Roth, adding that such systems are especially concerning when they stall.
“This at least will show some progression,” he said. “It won’t be as bad as some of the multiday heavy rain events that the mountains of California can sometimes get.”
The system is expected to reach the Great Lakes by Wednesday, when thunderstorms will most likely become more scattered and less intense. However, a lower-level risk for flash flooding, 1 out of 4, was expected across parts of the Carolinas and into southern Pennsylvania through Thursday.
Nazaneen Ghaffar is a Times reporter on the Weather team.
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